The present invention relates to a lubricating oil for a refrigerator using 1,1,1,2-tetrafluoroethane, and in particular, to a lubricating oil for a refrigerator having excellent compatibility with the refrigerant and having a low hygroscopic property, high thermal stability and lubricating property.
As conventional refrigerants for refrigerators, R11 (CCl.sub.3 F) is used for air-conditioning systems in buildings, and R12 (CCl.sub.2 F.sub.2) is used for electric refrigerators or as a refrigerant for automotive air-conditioning systems of the rotary type or reciprocating type. With the controversial problem of the destruction of ozone in the stratosphere, the development of an alternative substance is imminently needed.
In recent years, R123 (CF.sub.3 CHCl.sub.2) has been studied as a possible alternative for R11, but some problems remain such as hiqh price or the lack of a toxicity test. On the other hand, R22 (CHClF.sub.2) is now being considered as an alternative for R.sub.12 because of its easiness to decompose. However, the operating pressure at normal temperature is high because of low boiling point, and pressure-resistant hardware is therefore needed. Also, there are the problems of leaking from packings and hose components as well as the problems of low electric insulating property.
On the other hand, 1,1,1,2-tetrafluoroethane (R134a), known as an alternative for R12, does not contain chlorine which causes ozone destruction, and has passed the acute and subacute toxicity tests. Thus, attention is now focused on its application.
At present, a polyether synthetic oil having high viscosity is under development as lubricating oil for refrigerators. The operating temperature of a lubricating oil for a refrigerator is normally between -30.degree. and 100.degree. C. When a polyether synthetic oil is mixed with 1,1,1,2-tetrafluoroethane refrigerant, these substances separate from each other at high temperature, and it has also problems in hygroscopic property and lubricating property.
The requirements for lubricating oils for refrigerators are: wide temperature range for compatibility with the refrigerant (compatibility), i.e., no clouding at high temperature (high solvation of the refrigerant to the lubricating oil), high molecular polarity of the lubricating oil, no separation of the lubricating oil from the refrigerant at low temperature (high solubility of the lubricating oil to the refrigerant, and low molecular weight of lubricating base oil). For this reason, high compatibility with the refrigerant is very important, and it is necessary that the substance is not separated from the refrigerant at high or low temperatures and that it does not react with it. If the compatibility with the refrigerant is low, the equipment may seize on the portion of the refrigerator which is subject to high temperature.
The range of viscosity suitable for a lubricating oil for a refrigerator differs according to each type of refrigerator, and a lubricating oil having suitable viscosity is desirable.
Further, the lubricating oil for a refrigerator must not be corrosive to the refrigerating equipment, must not be reduced of its insulating property, and must have high stability to the refrigerant.
Also, the lubricating oil for a refrigerator must improve the wear-resistant property of aluminum components in piston and bearings, made of iron and aluminum, of the refrigerator.
The object of the present invention is to provide a lubricating oil for a refrigerator suitable for the use in the refrigerator using 1, 1, 1, 2-tetrafluoroethane refrigerant, having a wide compatibility temperature range with the refrigerant, having no corrosive property to refrigerating equipment, showing no reduction in insulating property, having a high stability to the refrigerant and improving the wear-resistant property of equipment components.